1. Field of the Invention
The present invention relates to an electromagnetic induction type encoder, and in particular to a highly accurate and inexpensive electromagnetic induction type encoder that is preferably used for calipers, indicators, linear encoders, micrometers, etc., and is capable of obtaining strong signal intensity with offset reduced by a short scale coil, and is durable against fluctuations in the yaw direction.
2. Description of the Related Art
As has been described in Japanese Published Unexamined Patent Application No. H10-318781 (hereinafter, referred to as Patent Document 1) and Japanese Published Unexamined Patent Application No. 2003-121206 (in particular, FIG. 1, FIG. 2, and FIG. 3) (hereinafter, referred to as Patent Document 2), as an example of Patent Document 2 shown in FIG. 1, such an electromagnetic induction type encoder has been known, which includes a number of scale coils 14,16 arrayed on a scale 10 along the measurement direction, and transmitting coils 24,26 and receiving coils 20, 22 disposed on a grid (may be referred to as a slider, too) 12 relatively movable in the measurement direction with respect to the scale 10, and is capable of detecting a relative movement amount of the scale 10 and the grid 12 from changes in magnetic fluxes detected by the receiving coils via the scale coils when the transmitting coils are magnetized. In the drawing, reference numeral 28 denotes a transmission control portion, and reference numeral 30 denotes a receiving control portion.
Where offset being excessive signals is in an attempt to be reduced in such an electromagnetic induction type encoder, as shown in FIG. 2, the offset has been reduced by disposing the receiving coils 20 at a portion (that is, in the example of FIG. 2, the middle part between both side transmitting coils) where the magnetic fields generated by the transmitting coils 24 are cancelled and is substantially brought to zero. Also, in Patent Document 2, the second receiving coils 22 are also disposed at both sides of the second transmitting coil 26 as shown in FIG. 3, in addition to such a configuration composed of the first transmitting coils 24 in FIG. 2 and the first receiving coil 20 therein.
However, with the configuration, three rows of scale coils are required, wherein there arises a problem in that, since the wiring of the scale coils is lengthened, induction current generated attenuates due to impedance of the scale coil itself and intensive signals are hardly obtained.